#include <cstdio>
#include <algorithm>
using namespace std;

const int NMAX = 1010, WMAX = 5010, INF = 0x3f3f3f3f;

int N, W, E[NMAX], C[NMAX], MinCost[2][WMAX], Past, Current, Ans = INF;

int main()
{
    freopen("energii.in", "r", stdin);
    freopen("energii.out", "w", stdout);

    scanf("%i %i", &N, &W);
    for(int i = 1; i <= N; ++ i) scanf("%i %i", &E[i], &C[i]);

    for(int i = 1; i <= WMAX; ++ i)
        MinCost[0][i] = INF;

    Current = 1;

    for(int i = 0; i < N; ++ i)
    {
        for(int j = 0; j <= W; ++ j)
            MinCost[Current][j] = INF;

        for(int j = 0; j <= W; ++ j)
        {
            MinCost[Current][j] = min(MinCost[Current][j], MinCost[Past][j]);
            if(j + E[i + 1] >= W) Ans = min(Ans, MinCost[Past][j] + C[i + 1]);
            else MinCost[Current][j + E[i + 1]] = min(MinCost[Current][j + E[i + 1]], MinCost[Past][j] + C[i + 1]);
        }

        Current ^= 1;
        Past ^= 1;
    }

    if(Ans == INF) printf("-1\n");
    else printf("%i\n", Ans);
}